The invention relates to a glass ceramic mass, comprising at least one oxide ceramic, containing barium, titanium and at least one rare earth metal Rek and at least one glass material, containing at least one oxide with boron, at least one oxide with silicon and at least one oxide with at least one bivalent metal Me2+. In addition to the glass ceramic mass, an application of the glass ceramic mass is described.
A glass ceramic mass of the aforementioned type is known from U.S. Pat. No. 5,264,403. The oxide ceramic for the known glass ceramic mass is manufactured from barium oxide (BaO), titanium dioxide (TiO2), a trioxide of a rare earth metal (Rek2O3) and possibly bismuth trioxide (Bi2O3). The rare earth metal Rek is for example neodymium. The glass material in the glass ceramic mass consists of boron trioxide (B2O3), silicon dioxide and zinc oxide (ZnO). A ceramic proportion of the oxide ceramic in the glass ceramic mass is for example 90% and a glass proportion of the glass material 10%.
A compression of the glass ceramic mass occurs at a sintering temperature of about 950° C. The glass ceramic mass is thus suitable for use in LTCC (low temperature cofired ceramics) technology. The LTCC technology is described for example in D. L. Wilcox et al, Proc. 1997 ISAM, Philadelphia, pp. 17 to 23. The LTCC technology is a ceramic multilayer method in which a passive electrical component can be integrated in the volume of a ceramic multilayer body. The passive electrical component is for example an electrical conductor track, a coil, an induction or a capacitor. Integration is achieved, for example, by printing a metal structure corresponding to the component on one or more ceramic film blanks, stacking the printed ceramic film blanks above one another to form a composite and sintering the composite. Since ceramic film blanks are used with a low sintering glass ceramic mass, electrically highly conductive elementary metal Me0 with a low melting point such as silver or copper can be sintered in a composite with the ceramic film blank. In this situation, the functional integrity of the component integrated through the use of LTCC technology is crucially dependent on the dielectric material properties of the glass ceramic used. A material property of this type is for example the permittivity (εr), a quality factor (Q) and a temperature coefficient of frequency (Tf value).
With regard to the known glass ceramic mass, the glass proportion is relatively low, with the result that compression of the glass ceramic mass takes places as a result of reactive liquid phase sintering. During the sintering process, a liquid glass phase (glass melt) is formed from the glass material. At a higher temperature the oxide ceramic dissolves in the glass melt until a saturation concentration is reached and a separation of the oxide ceramic occurs once again. As a result of the oxide ceramic dissolving and separating out again, the composition of the oxide ceramic and thus also the composition of the glass phase or the glass material can change. During cooling, crystallization from the glass melt can additionally occur. For example, in this situation one constituent of the oxide ceramic remains in the glass phase after cooling of the glass ceramic mass. If the composition of the oxide ceramic and thus also the composition of the glass material changes as a result of compression, it is difficult to define the material. properties of the compressed glass ceramic mass and thus to guarantee the functional integrity of the component integrated through the use of LTCC technology.